Thermodynamic refrigerator

ABSTRACT

A cryogenic refrigeration apparatus operable in accordance with a thermodynamic cycle such as the Vuilleumier cycle, wherein the hot and cold chambers are physically separated, and the corresponding hot and cold displacers are driven reciprocally by separate motors. Proper pressure variations and phase difference between the motions of the displacers and the gas transported are maintained preferably by synchronizing the speeds of the different motors.

United States Patent [72] inventors Alexander Daniels Briarcliff Manor;Frits Karel du Pre, White Plains, both of N.Y. [21] Appl. No. 14,040[22] Filed Feb. 25, 1970 [4S] Patented Dec. 28, 1971 [73] Assignee U.S.Phillips Corporation New York, N.Y.

[54] THERMODYNAMIC REFRIGERATOR 12 Claims, 5 Drawing Figs.

[52] U.S. Cl 62/6, 62/86 [51] Int. Cl F25b 9/00 [50] Field of Search62/6, 86

[56] References Cited UNITED STATES PATENTS 1,275,507 8/1918 Vuilleumier62/6 THERMAL COMPRESSOR MOTOR 3| 0 EXCHANGER 3,237,42l 3/1966 Gifford62/6 3,302,422 2/1967 Smith 62/6 3,314,244 4/ l 967 Green 62/6 3,379,0264/1968 Cowans 62/6 3,423,948 1/1969 Cowans..... 62/6 3,431,746 3/1969Webster.... 62/6 Primary ExaminerWilliam J. Wye Att0rney Frank R.Trifari COLD FINGER HEAT 3| 27 MOTOR "spur CYCLE" VM PATENTED M02819?!SHEET 1 BF 2 INVIZNIORS. ALEXANDER DANIELS FRITS KAREL duPRE AGENT xOnm$23000 3- zopunooma 0400 PATENTEDDEC28l97l 3 4 same [If 2 HOT DISLACER oTHERMAL HEAT 77 K COMPRESSOR cow 1M J32 FINGER 2| 25 33 HEAT 2; l5,l6|3',|4' Ex 2e REGULARIVM' "SPLIT'CYCLE" v ,Fig. 2 Fig. 3

Fig. 5

INVENTORS. ALEXANDER DANIELS FRITS KAREL duPRE THERMODYNAMICREFRIGERATOR BACKGROUND OF THE INVENTION This invention is in the fieldof cyogenic refrigeration apparatus and thermodynamic cycles on whichsuch apparatus operate, and particularly the field of refrigerationmeans operating on a cycle such as the Vuilleumier regenerative cycle asrelated to the idealized Stirling cycle.

In refrigeration apparatus operating on a Stirling regenerative cycle,there are typically five interconnected elements, namely a compression"space, a cooler, a regenerator, a freezer, and an expansion space. Insuch devices the helium gas, working medium is first compressed in thecompression space, then cooled in the cooler, and next flowed through aregenerator where additional heat from the gas is extracted and stored.Upon exiting the regenerator the gas flows into the expansion chamberwhere cold is produced and finally extracted by means of a freezercomponent. Subsequently, the gas is returned through the regenerator,where it reabsorbs the stored heat and flows again to the compressionchamber to complete a cycle.

Although ideally three elements (compression space, regenerator, andexpansion space) are sufficient to explain the operation of such cycles,in most practical machines, the cooler and freezer elements have beenadded in order to effect adequate heat transfer between the gas in thecompression and expansion spaces and the surroundings; the cooler andfreezer elements thus compensate for the poor thermal contact and heattransfer capability between the working gas and the two cylinders. Inthe Stirling cycle apparatus as thus described, there is establishedvariable volume compression and expansion spaces having differentaverage temperatures, with a motor provided to drive the displacers in asuitable phase relationship, whereby the gas is successively compressedand expanded.

The Vuilleumier cycle differs from the Stirling cycle primarily in itsmeans for establishing pressure variations in the gas for compressionand expansion. In known Vuilleumier cycle refrigerators, there arewithin a single housing, two chambers and a connecting duct, a displacerpiston reciprocally movable in each chamber, and a single electric motorwith a dual connecting rods for driving the two displacers at exactlythe same speed and in a 90 or other phase difference. Heat is added intoone chamber with a higher gas pressure resulting in the working space,thus establishing a thermal compressor in substitute for the mechanicalcompressor of the Stirling cycle. In this Vuilleumier device the heatedand compressed gas flows from the hot space through regenerator materialin the corresponding displacer, through the connecting duct whichincludes heat exchanger means to transfer heat to the ambient, thenthrough a second regenerator in the cold chamber displacer, with coldfinally produced in the remote space of the nonheated cylinder.

The pressure variations in the cold volume of this Vuilleumier deviceare produced by the motion of the hot displacer in the following way. Ifthe hot displacer is down, much of the helium is in the hot area, theaverage helium temperature will be high, and the pressure will be higheverywhere in the working space. On the other hand, if the displacer isup," very little of the helium is in the hot area, the average helium.temperature will be low, and the pressure will be low. Therefore, aslong as the hot displacer moves up and down in the correct phaserelationship to the motion of the cold displacer, the required pressureand volume variations are produced in the cold expansion space, and coldis produced according to the equation of Q=jpdV; this equation definescold production per period in the various thermodynamic cycles, with thesame cold produced in a given expansion volume no matter how thepressure variation is produced.

A further characteristic of the Vuilleumier refrigerator is that thepower required to drive the displacers may be small, since the onlyforces on the displacers are those due to the pressure drop of thehelium flowing through them and to the mechanical friction. Furthermore,since there is a heat input at the hot chamber and at the cold fingerwhere an object is cooled, it follows that the heat rejection to theambient equals the sum of these amounts, plus the small amount of heatequal to the motor input.

The above equation for cold production should be considered with respectto conditions on which it is based, namely the cold production duringone cycle in a volume into which (and out of which) a gas can flow onlyvia an ideal regenerator. This is the situation encountered in both theidealized Stirling and Vuilleumier regenerative cycles, with thesecycles differing only in the way they produce the periodic pressurevariations, since the cold-volume variations are always due to asinusoidal motion of a displacer piston. One of the unique features ofthe Vuilleumier refrigerator is that its constant volume process with nomechanical compression, results in low bearing loads, long mechanicallike, and quiet operation; also such construction is compact and hasminimized dead space, as shown in the drawings.

Known Vuilleumier cycle refrigerators are constructed generally asdescribed above, with the stated features and advantages; however, suchapparatus has a number of major limitations and disadvantages. Sinceboth hot and cold dis-Q placers are contained within a single housing,it is inherent in the apparatus design that the heat source applied tothe hot chamber is in close proximity to the cold chamber. In situationswhere the source of heat is available only at a point remote from theplace where cold production is to be provided, a long heat pipe would berequired to bring the heat to the hot chamber, with correspondingexpense and complications; in such cases, the Vuilleumier cyclerefrigerator would not be desirable. Furthermore, there are now varioussituations calling for cold production in a given location, with thedissipation of any heat into this area being intolerable. Thus thepresence, near the cold production area, of the heat source, or the hotchamber, or even a heat pipe would render prior Vuilleumierrefrigerators impractical.

Another limitation in these devices concerns the cyclic pressurevariations of the gas caused by movement of the displacers with a properphase difference. To achieve this phase relationship while cycling thehot and cold displacers at the same speed, known devices use a singlemotor with dual connecting rods. Since it has been established that thecold displacer must be reciprocated relatively slowly to minimize flowlosses therein, a consequence is an equally slow-running hot displacerand resulting design inflexibility.

SUMMARY OF THE INVENTION The present invention is an improvement of theVuilleumier cycle refrigerator apparatus which overcomes the variousstructural and functional limitations described above in the prior art.To accomplish these improvements the basic structure of a typical knownVuilleumier refrigerator has been so significantly altered that the hotand cold cylinders are physically separated, with an independentelectric motor drive means for each. With this new arrangement the hotand cold displacers can be operated by motors having synchronized speedsor different speeds; and both the hot chamber and the heat source may belocated quite remote from the area of cold production. Where the newapparatus has motors operable at different speeds, the hot and coldchambers interconnected by tubes, include valves synchronized with eachdisplacer, whereby the desired pressure variations in the gas areobtained. Also connected between the hot and cold sides can be anadsorber to remove contaminants of the flowing gas stream. In a furtherembodiment, a single thermal compressor formed by a hot-side cylinder,displacer, and electric motor, may cooperate with a plurality of remotecold fingers. In each of the above embodiments the cold and hot chambersand their associated displacers and drive means are designed to bephysically separated and independent of each other, except forinterconnecting duct means.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic view of a priorart Vuilleumier cycle refrigeration apparatus.

FIG. 2 is a schematic view of apparatus similar to that of FIG. 1.

FIG. 3 is a schematic view of the new split-cycle refrigera- 101.

FIG. 4 is a further embodiment of the new invention in FIG. 3.

FIG. 5 is a further embodiment of the invention in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in FIG. I, the priorart Vuilleumier cycle refrigerator has a hot chamber 1 l a cold fingerl2, and a connecting duct 13 and cooler 14. FIG. 2 is similar with hotand cold sides 11' and 12 and a combination duct and cooler 13' and 14'.Within each hot chamber is displacer l5 and its internal regenerator l6,and within each cold finger is its displacer and regenerator l7 and 18.A single electric motor 19 drives the two displacers in FIGS. 1 and 2 atthe same speed, in a 90 phase relationship. The apparata thus describedare closed systems, each within a single housing 20. Disposed about aportion of the hot cylinders 11, 11' is shown a heat exchanger 21 fortransferring heat from an external source into the hot chamber andheating the gas therein.

As shown in FIG. 1 the cyclic gas flow pattern is as follows. After thegas is heated in chamber 11 with a resulting pressure increase, it flowsthrough regenerator 16 to heat exchangers 14 where it is cooled, thenthrough regenerator 18 to expansion space 12a with resulting coldproduction. A freezer element not shown would be used to transfer thecold to a device or area to be refrigerated and the gas then returns tocomplete the cycle.

Motor 19 has two connecting rods 22 and 23 for driving the hot and colddisplacers respectively at the same speed, and at a 90 phase differencewhich might be varied as required. In the device disclosed coldproduction of 1 watt at 77 K. would be achieved with a heat input of 115watts at 1,000 K., 5 watt motor, and intermediate cooling at 350 K.

The first shown embodiment of the new invention in FIG. 3 has a thermalcompressor 25 and its motor 26, and a separate cold finger 27 with itsmotor 28. While the motors are physically separated, they are operatedat the same speed, so that the reciprocal movements of the thermalcompressor displacer 29 and the cold finger displacer 30 will also beidentical, but at a suitable phase difference. One preferable method forattaining synchronized operation of the motors with a selected phasedifference would be to use electronic control means.

Interconnecting the hot and cold sides 25 and 27 is a single duct 31;with this arrangement the gas will be cyclically moved between the hotand cold sides with the desired pressure variations, with no requirementfor valves to control the gas flow. Also present is heat exchanger 32,either separate or part of duct 31, for transferring heat from anexternal source into the hot chamber 25 and a second heat exchanger 33for removing certain heat of compression before the gas is expanded inthe cold finger. Any heat rejection associated with the thermalcompressor and its associated motor, and any vibrations from theseelements may be isolated from the cold finger, and also may be spacedquite remotely. It is also possible to replace the thermal compressor 25with a different, mechanical compressor, and still retain the otherstructural features described above.

A variation of the embodiment of FIG. 3 is shown in FIG. 4 where motors40 and 41 for the thermal compressor 42 and the cold finger 43respectively are run at different speeds, preferably with the coldfinger displacer at a low speed to minimize flow losses and the hotdisplacer at a relatively higher speed as determined by designconsiderations. When the motors are run at different speeds, the desiredcyclic gas pressure variations will be obtained by synchronizing valves44, 45, 46 and 47 with the displacer movements. These valves areassociated with pressure chamber 48 wherein the higher pressure gas isstored and cyclically released to the cold finger and a low-pressurechamber 480. Heat exchanger 49 provides cooling for the gas subsequentto its heating and pressure stage in the hot chamber 42.

A still further embodiment of the present invention is shown in FIG. 5where there are two thermal compressors 50 and 51 driven by a singlemotor 42. Connected to each compressor is a pair of cold fingers 53, 54and 55, 56. Since each of the four cold fingers has its own electricmotor, interdependent of, but synchronized with the compression drivemeans 52, there will be cold production by the cold fingers at aplurality of locations, all remote from the heat source and from thethermal compressors, without a need for valves.

In any of the above embodiments an adsorber, 31a may be added in theconnecting duct 31 of FIG. 3 between the hot and cold sides, forremoving contaminants in the gas as it flows cyclically. From the pointof view of flexibility in use, these and other embodiments may utilizevarious heat sources, including electrical heat, propane, and isotopes.

What is claimed is:

l. Thermodynamic apparatus operable in accordance with the Vuillemierregenerative cycle with a heat source comprismg:

a. a thermal compressor formed of a hot chamber defining therein aheating space, a hot displacer reciprocally movable in the hot chamber,first drive means connected to the hot displacer for driving same, andfirst heat exchange means for transferring heat from said heat sourceinto said heating space,

b. a cold finger formed ofa cold chamber defining therein a gasexpansion space and being physically separated from the hot chamber, acold displacer reciprocally movablein the cold chamber, and second drivemeans being connected to the cold displacer for driving same and beingindependent of the first drive means, the expansion space having a loweraverage temperature than the heating space average temperature.

0. duct means interconnecting the hot and cold chambers, with a workingmedium flowable cyclically through the duct between said spaces,

d. second heat exchange means associated with the duct for cooling sameby transferring heat from the medium flowing therethrough to ambient,and

e. a regenerator associated with each displacer through which theworking medium flows.

2. Apparatus as defined in claim 1 wherein the hot and cold chambers areformed by cylinders having corresponding bores in which the displacersare reciprocated.

3. Apparatus as defined in claim 1 wherein the drive means are electricmotors which are synchronized to attain the same speeds and a selectedphase difference.

4. Apparatus as defined in claim 1 wherein the first and second drivemeans are electric motors, the first drive means is operated at a higherspeed than the second, the apparatus further comprising valve meanssynchronized with the drive means for controlling the gas flow andpressure variations of said gas.

5. Apparatus as defined in claim 1 further comprising a second coldfinger and second duct means interconnecting the second cold finger withthe thermal compressor.

6. Apparatus as defined in claim 1 comprising a second thermalcompressor, and auxiliary drive means interconnecting the first drivemeans and the second compressor, the first and auxiliary drive meansbeing opposed and balanced to minimize vibration.

7. Apparatus as defined in claim 1, further comprising valve means forcontrolling communication of each of said chambers with said duct means,operation of the valves being synchronized with the two drive means toprovide the desired phase difference between the displacer motion andthe pressure variation.

8. Apparatus as defined in claim 1 further comprising an adsorberconnected between said chambers for removing contaminants from the gasflowing through the adsorber.

9. Apparatus as defined in claim I wherein each regenerator is disposedwithin a displacer.

10. Apparatus operable in accordance with a thermodynamic regenerativecycle such as the Vuilleumier and Stirling cycles, and with a heatsource comprising:

a. compression means including a compression chamber defining therein acompression space, a piston reciprocally movable in the chamber, andfirst drive means connected to the piston for driving same,

b. a cold finger formed of a cold chamber defining therein an expansionspace and being physically separated from the compression chamber, acold displacer reciprocally movable in the cold chamber, and seconddrive means being connected to the cold displacer for driving same andbeing independent of the first drive means, the exmeans are electricmotors.

12. Apparatus as defined in claim 10 wherein the regenerator is disposedwithin the displacer.

1. Thermodynamic apparatus operable in accordance with the Vuillemierregenerative cycle with a heat source comprising: a. a thermalcompressor formed of a hot chamber defining therein a heating space, ahot displacer reciprocally movable in the hot chamber, first drive meansconnected to the hot displacer for driving same, and first heat exchangemeans for transferring heat from said heat source into said heatingspace, b. a cold finger formed of a cold chamber defining therein a gasexpansion space and being physically separated from the hot chamber, acold displacer reciprocally movable in the cold chamber, and seconddrive means being connected to the cold displacer for driving same andbeing independent of the first drive means, the expansion space having alower average temperature than the heating space average temperature. c.duct means interconnecting the hot and cold chambers, with a workingmedium flowable cyclically through the duct between said spaces, d.second heat exchange means associated with the duct for cooling same bytransferring heat from the medium flowing therethrough to ambient, ande. a regenerator associated with each displacer through which theworking medium flows.
 2. Apparatus as defined in claim 1 wherein the hotand cold chambers are fOrmed by cylinders having corresponding bores inwhich the displacers are reciprocated.
 3. Apparatus as defined in claim1 wherein the drive means are electric motors which are synchronized toattain the same speeds and a selected phase difference.
 4. Apparatus asdefined in claim 1 wherein the first and second drive means are electricmotors, the first drive means is operated at a higher speed than thesecond, the apparatus further comprising valve means synchronized withthe drive means for controlling the gas flow and pressure variations ofsaid gas.
 5. Apparatus as defined in claim 1 further comprising a secondcold finger and second duct means interconnecting the second cold fingerwith the thermal compressor.
 6. Apparatus as defined in claim 1comprising a second thermal compressor, and auxiliary drive meansinterconnecting the first drive means and the second compressor, thefirst and auxiliary drive means being opposed and balanced to minimizevibration.
 7. Apparatus as defined in claim 1, further comprising valvemeans for controlling communication of each of said chambers with saidduct means, operation of the valves being synchronized with the twodrive means to provide the desired phase difference between thedisplacer motion and the pressure variation.
 8. Apparatus as defined inclaim 1 further comprising an adsorber connected between said chambersfor removing contaminants from the gas flowing through the adsorber. 9.Apparatus as defined in claim 1 wherein each regenerator is disposedwithin a displacer.
 10. Apparatus operable in accordance with athermodynamic regenerative cycle such as the Vuilleumier and Stirlingcycles, and with a heat source comprising: a. compression meansincluding a compression chamber defining therein a compression space, apiston reciprocally movable in the chamber, and first drive meansconnected to the piston for driving same, b. a cold finger formed of acold chamber defining therein an expansion space and being physicallyseparated from the compression chamber, a cold displacer reciprocallymovable in the cold chamber, and second drive means being connected tothe cold displacer for driving same and being independent of the firstdrive means, the expansion space having a lower average temperature thanthe heating space average temperature, c. means for synchronizing thespeed of the two drive means at a selected phase difference, d. ductmeans interconnecting the compression and cold chambers, with a workingmedium flowable cyclically through the duct between said spaces, e.second heat exchange means associated with the duct for cooling same bytransferring heat from the medium flowing therethrough to ambient, andf. a regenerator associated with the displacer through which the workingmedium flows.
 11. Apparatus as defined in claim 10 wherein said drivemeans are electric motors.
 12. Apparatus as defined in claim 10 whereinthe regenerator is disposed within the displacer.